1. Field of the Invention
The present invention relates to an inkjet recording apparatus which is capable of ejecting particulate matter such as pigment matter and toner matter by making use of an electric field, and more particularly to control for the inkjet recording apparatus.
2. Description of the Related Art
There has recently been a growing interest in non-impact recording methods, because noise while recording is extremely small to such a degree that it can be neglected. Particularly, inkjet recording methods are extremely effective in that they are structurally simple and that they can perform high-speed recording directly onto ordinary medium. As one of the inkjet recording methods, there is an electrostatic inkjet recording method.
The electrostatic inkjet recording apparatus generally has an electrostatic inkjet recording head and a counter electrode which is disposed behind the recording medium to form an electric field between it and the recording head. The electrostatic inkjet recording head has an ink chamber which temporarily stores ink containing toner particles and a plurality of ejection electrodes formed near the end of the ink chamber and directed toward the counter electrode. The ink near the front end of the ejection electrode forms a concave meniscus due to its surface tension, and consequently, the ink is supplied to the front end of the ejection electrode. If positive voltage relative to the counter electrode is supplied to a certain ejection electrode of the head, then the particulate matter in ink will be moved toward the front end of that ejection electrode by the electric field generated between the ejection electrode and the counter electrode. When the coulomb force due to the electric field between the ejection electrode and the counter electrode considerably exceeds the surface tension of the ink liquid, the particulate matter reaching the front end of the ejection electrode is jetted toward the counter electrode as an agglomeration of particulate matter having a small quantity of liquid, and consequently, the jetted agglomeration adheres to the surface of the recording medium. Thus, by applying pulses of positive voltage to a desired ejection electrode, agglomerations of particulate matter are jetted in sequence from the front end of the ejection electrode, and printing is performed. A recording head such as this is disclosed, for example, in PCT International Publication No. WO93/11866.
According to the conventional inkjet recording head, however, the respective ejection electrodes are independently driven by drivers supplying driving voltages depending on input data (see FIG. 4 and page 9, lines 21-31, of the above publication No. WO93/11866). Especially, in the case of a multi-head having an array of dozens of heads or a line head having a linear array of hundreds to thousands of ejection electrodes, it is necessary to provide driver circuits as many as the ejection electrodes, resulting in complicated circuit configuration and the increased amount of hardware. This causes the size and cost of the recording apparatus to be increased.
Further, variations in the positions and shapes of the ejection electrodes inevitably occur in practical manufacturing processes. In such cases, an amount of pigment matter (or toner matter) ejected from an ejection electrode is different from that of another ejection electrode even when the same driving voltage is applied to them, resulting in deteriorated quality of an image formed on a recording medium. More specifically, in the case where an ejection electrode has a more acute tip angle, the electric field is more likely to be concentrated thereon. Therefore, the increased amount of pigment matter is ejected from that ejection electrode, resulting in a larger ink dot formed on a recording paper. Similarly, in the case of variations in distance between an ejection electrode and the counter electrode, the smaller the distance, the larger the ink dot. Furthermore, the electric field is more likely to be concentrated on the ejection electrodes located at both ends, which causes the ink dots at both ends to increase in size. Such variations in ink dot size become more pronounced with the number of ejection electrodes.